Driver-assistance systems for motor vehicles have, for instance, three basic application fields.
The first of these is the so-called pre-crash control which is meant to detect the imminent occurrence of a collision of the vehicle with an object and to activate, or precondition, occupant safety systems of the vehicle just prior to the actual occurrence of the collision, in this way protecting the occupants from the results of the accident to the greatest possible extent.
A second application field is the so-called park distance control. Park distance controls are provided for detecting objects in the immediate vicinity of the vehicle with which it may collide, given low vehicle speed and situations that are difficult to assess, and to bring these to the driver's attention.
A third application relates to cruise-control systems, also known as adaptive cruise control (ACC), which detect the distance to adjacent vehicles when driving in a queue and adapt the speed of the vehicle to that of an adjacent one, so that driver stress may be reduced in heavy traffic.
Although these three applications have in common that their implementation in each case requires at least one sensor for measuring the distance of the vehicle from an object and a control unit for activating functional groups of the vehicle as a function of the measuring result of the sensor, it is difficult, nevertheless, to integrate a plurality of these applications into a unified system in such a way that the driver actually has the unrestricted use of these various systems.
The reason for this is that the demands of the three applications on the measuring results of the sensor, which the control unit requires, and the spatial expansion of the area to be monitored vary widely. For instance, in the park-distance control operating mode, distance information for a distance range of generally less than 1.5 m is required, relatively long time periods of several 10 milliseconds being available for the detection. On the other hand, the distance resolution of these measuring results must be in the range of 10 cm or less. The spatial area to be monitored not only includes the area in the front and the rear of the vehicle in extension of the vehicle center axis, but also those areas lying considerably beyond this axis, since it is normal to drive tight curves when parking and it is possible, therefore, for a vehicle to collide with objects that are next to it, in front or behind it, away from its instantaneous driving direction. In an ACC system, the distance range that is of interest is usually between a few meters to a few 10 m in front of the vehicle. In a pre-crash system, it is generally desirable to monitor any direction from which a potentially dangerous object may approach. The distance range that is of interest is very wide since a potentially dangerous object, depending on its own velocity and that of the vehicle, should be detected and monitored already within a distance of up to several 10 meters, it possible. Small distances also require precise measurements, in order to accurately predict the actual collision time and to be able to ensure that the safety systems are not activated unintentionally when the vehicle merely passes in close proximity to an object that was detected as dangerous and which is monitored by the pre-crash system, without colliding with it.
Due to these different demands, driver-assistance systems are generally designed for no more than one of the mentioned application areas. While it would be conceivable to create a driver-assistance system that lets a driver switch between a plurality of operating states corresponding to the mentioned applications, this would entail the considerable disadvantage, however, of only one of the three safety systems being available at any given time. This means that no pre-crash protection would be available if such a driver-assistance system were used for an ACC-control, and vice versa. An especially dangerous moment in such a system would also result if the driver, depending on the driving situation, neglected to select the appropriate operating mode, thus considering himself safe, when this is actually not the case.